Are Automator services not pluggable to 3rd party apps anymore?

In Mavericks and Lion I am able to inject any service into any native and 3rd party application. As of High Sierra, I no longer can do that. I created a service to receive text clipping in Safari and Firefox, but when I select text in either of them only in Safari do I see the service in the pulldown under the “Services” submenu. In Firefox I do not. It’s interesting that the both services show up in Safari when text is selected though only one of them should.

Why? Is it an established new law from now on?

Model: MacBook Pro
AppleScript: 2.7
Browser: Safari 605.1.15
Operating System: macOS 10.13